The invention relates to a method and a device for isolating points of an electrically conductive flow medium having a different electrical potential along its flow path, for example in an electrostatic painting system.
Methods and devices of the known art are technically complex, particularly if the flow medium is at ground potential at the beginning of its flow path and has high voltage applied to the flow medium at the end of its flow path. Such relationships dominate, for example, in electrostatic painting systems that process water-thinnable paints or lacquers, as are used, for example, in automobile manufacturing. In such electrostatic painting systems, paint or lacquer material is guided through a conduit or line to an atomizer or spray apparatus that is under a high voltage potential. If this paint or lacquer material is electrically conductable, it is important that an electrical short does not occur along the paint supply line, as the other end of the paint supply line is at ground potential. For this reason, a high voltage potential must also be applied to the paint supply line and the corresponding paint containers and the line, and the containers must be secured in a high voltage area to which access is prohibited. This, on the other hand, has as a consequence that the containers cannot be refilled from a supply line that is at ground potential during operation. As a result, the paint operation must be interrupted during the refilling procedure.
In order to ensure a continuous supply of the paint or lacquer material from a container under a high voltage potential to the atomizer or spray apparatus, the container must be filled discontinuously with paint or lacquer material in a suitable manner. This is in fact the actual practice with existing paint systems. As a further complication, generally several different colors or tones of the conductive paint or lacquer such as, for example, water-based lacquer, must be held ready for delivery to an atomizer or spray apparatus that is under high voltage via an automatic color changer. If voltage isolating devices are used between the color changer and the atomizer or spray apparatus, it is known that it is then impossible to quickly automatically flush all the components if the voltage isolating devices allow only short distances between the components under different potential during the painting operation, and if the devices are also to be constructed as compactly as possible.
In order to provide the necessary isolation in view of the governing potential between the components that are under high voltage and at ground potential, relatively large spaces or distances in the range of greater than 200 mm must be adhered to during the painting operation. Otherwise, the components cannot be switched between the inputs and outputs during the grounded operation, free of high voltage, to allow an automatic quick color change or a flushing cycle to be carried out.
It is, therefore, an object of the invention to provide measures that will allow a particularly practical handling and reliable isolation between points of the flow path and/or of the electrically conductive flow medium that are under different potential.
The above objects have been achieved according to the invention in a voltage blocking device for conveying an electrically conducting fluid therethrough, comprising: a housing including a housing outer wall and a first intermediate wall, wherein a first chamber and a second chamber are provided on opposite sides of the first intermediate wall within the housing outer wall, and wherein an annular receiving channel and an outlet opening are provided in the housing; an electrically insulating liquid contained in the second chamber; a movable nozzle needle having a free first end that is movably arranged in the housing and that has therein at least one radially extending discharge opening, and having a longitudinal channel that extends longitudinally axially in the movable nozzle needle and that communicates with the at least one radially extending discharge opening, wherein the free first end of the nozzle needle is movable between a first position and a second position within the housing, and wherein the free first end in the second position is located in the second chamber containing the electrically insulating liquid; a first drive connected to the movable nozzle needle and adapted to move the movable nozzle needle selectively between the first position and the second position; a first closure member that is movably arranged and guided in the first intermediate wall so as to selectively open and close the annular receiving channel; and a second closure member that is movably arranged so as to selectively open and close the at least one radially extending discharge opening in the free first end of the nozzle needle. In a particular embodiment of the invention, the annular receiving channel and the outlet opening are especially arranged in the intermediate wall. According to another embodiment feature of the invention, a further annular drainage channel is provided axially next to the annular receiving channel.
With the inventive arrangement, this means that the electrically conductive flow medium flows inside of a lance or nozzle needle that has a discharge opening and that moves between an isolating position and a docking position which allows the transfer flow of the flow medium, and back again. The discharge opening remains closed until the docking position has been reached. Thus, the electrically conductive fluid does not come into contact with the contacting walls so that the danger is low that a film of electrically conductive fluid will build up on the contacting surfaces and then lead to a short-circuit. Furthermore, the voltage-blocking valve that serves as the voltage-blocking device preferably has an electrically non-conductive fluid in the chamber that receives the lance or nozzle needle (also called the valve needle herein).
The voltage-blocking valve according to the invention further comprises end pieces for the flow path that can be connected to each other and released from each other, whereby these end pieces are arranged at the same time in the electrically non-conductive fluid. It is therefore possible to provide a voltage-blocking device that satisfies high safety requirements, yet is small in size, is simple to use, provides great switching speed, and is also practical in its handling.